Kinetics of CO2 Sorption using ZK-4 zeolite

“We followed the physisorption of CO2 by monitoring the development of the υ1 + υ3 and υ1 + 2υ2 combination band at 3317 cm–1 with respect to time on zeolites Na-ZK-4 (1.8 and 2.8), NaK-ZK-4 (1.8), 28 at. % K+ (the sample with the highest CO2selectivity at Si/Al = 1.8), and NaK-ZK-4 (2.8), 55 at. % K+ (the sample with the highest CO2 selectivity at Si/Al = 2.8); see Figure 7. The zeolite Na-ZK-4 (2.8) had the fastest uptake of CO2, as shown in Figure 7, which was expected as it had only Na+ ions, which made the passage of CO2 more easy than that if K+ ions were present. The physisorption of CO2 on zeolite Na-ZK-4 (2.8) reached 60% of its maximum capacity already after 10 s. In the other two samples, the reduced CO2 physisorption rates were due to K+ ions populating the 8-rings. Specifically, zeolite NaK-ZK-4 (1.8) with 28 at. % of K+ had the slowest uptake of CO2, which took 10 min to reach 80% of its maximum CO2 physisorption capacity (i.e., after 24 h). This slow uptake rate was related to that K+ ions were present in the 8-rings of this zeolite and that the 6-rings were populated by Na+ and K+ ions. The CO2 adsorbing more rapidly on zeolite NaK-ZK-4 (2.8) 55 at. % than on zeolite NaK-ZK-4 (1.8) 28. at. % was ascribed to the smaller amount of Na+ and K+ cations in the 6-rings in the zeolite with a Si/Al ratio of 2.8.”


“Figure 7. Kinetics of CO2 physisorption on zeolites Na-ZK-4 (1.8, 2.8), NaK-ZK-4 (1.8) 28 at. %, and NaK-ZK-4 (2.8) 55 at. %.”

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